This invention relates to the field of earthworking tools. More specifically, this invention relates to those tools most suitable for the formation of notched blast holes.
A well known process useful in blasting is fracture control. It has been found that when an explosive charge is detonated in a notched blast hole, the presence of the notches causes the rock to fracture at the tips of the notches. The line of fracture would then proceed for some distance. In this way, the explosive force is directed so that overbreak is avoided.
It would be desirable from an economic standpoint to drill and notch the blast hole in a single pass. One of the earliest tools of this type used for fracture control is shown in U.S. Pat. No. 740,906, to Owen.
It is, of course, necessary that the tool perform dependably. A tool that becomes lodged in a blast hole, whether through breakage or improper design, is difficult and costly to remove. Often, if the tool does become lodged in a blast hole, the tool is considered lost and a new blast hole is drilled.
A modern version of the single-pass drilling and notching tool is illustrated in Department of Transportation Report No. UMTA-MA-06-0100-79-14, entitled "Field Evaluation of Fracture Control in Tunnel Blasting," at Page 31. It is to be noted that the tool illustrated is a conceptual sketch only.
A similar single-pass drilling and notching tool developed by the University of Maryland is illustrated in "Proceedings of the 22nd U.S. Symposium on Rock Mechanics," at Page 229, held at the Massachusetts Institute of Technology, June 29 to July 2, 1981. So far, this tool has only been found to be suitable for use in soft coal deposits.
It would be desirable to have a single-pass drilling and notching tool suitable for use in hard rock as well as in soft rock.
It is an object of this invention to have a single-pass drilling and notching tool that is dependable in use.
It is a further object of this invention to have a single-pass drilling and notching tool that is economical to use.
It is a still further object of this invention to have a single-pass drilling and notching tool that is suitable for use in both hard and soft rock.